Portable or wearable devices continue to increase in popularity, and feature increasingly sophisticated functionality, including wireless capabilities. Some of the devices may be used to monitor human body events like physical activity, gestures, speech, health, emotional state, etc. These events may be manifested by various bio-signals like electric (from skin conductivity and brain or muscle activity, etc.), mechanical (from tissue displacement or voice, etc.), temperature, and optical (from tissue and blood reflectance). Accordingly, in order to monitor such events, a device may be configured to measure a user's physiological context, such as respiration cycle, heart rate, temperature, or the like.
The performance of these applications may be related to the amount of information that may be obtained from the bio-signals. For instance, enhanced body activity tracking may be obtained if activity is sensed concurrently not only through inertial measurement units (IMUs) but also through electrocardiograms (ECG) and mechanomyograms (MMG). Similarly, gestures detection may be enhanced by concurrent use of IMUs, MMGs, photoplethysmograms (PPMG) and electromyograms (EMG). Emotional state may be monitored, for example, through concurrent electroencephalograms (EEG), functional near-infrared (fNIR) spectroscopy, PPMG (for pulse monitoring) and MMG (for respiration monitoring). Sensing multiple types of bio-signals may require using multi-modal bio-sensors. However, typical bio-sensors may transduce only one type of bio-signals.